1. Field of the Invention
The invention concerns the bending of glass plates into convex shape in a high-capacity convexing installation, entailing a possibility of simultaneous convexing of several, that installation being of the type in which a glass plate is brought to its bending (hereinafter, bending to assume a convex form will be referred to by the term "convexing") temperature, carried over a conveyor, stopped under an, upper transfer and/or convexing unit, picked up by that, upper unit and then released on a lower discharge and/or convexing unit after said plate is applied against the upper transfer and/or convexing unit.
2. Background of the Prior Art
It is known from U.S. Pat. Nos. 3,778,244; 4,813,993 and 4,682,997 how to use upper units capable of treating one glass plate at a time.
However, in order to increase production capacities when the convexed sheet glass manufactured is of small size, it is advantageous to bend several glass plates into convex shape simultaneously.
If the glass plates to be simultaneously treated are supplied on the conveyor arranged beside each other and the different stations available on a same upper unit are juxtaposed crosswise to the direction of feed of the conveyor, everything happens in the synchronization of operations, as in the case of a single glass plate. The different glass plates follow two exactly identical parallel paths and they must then undergo strictly identical convexing treatments.
That implies that the glass plates retain exactly identical relative positions all along their path; now, that can be difficult to obtain and it is impossible to correct, the position of just one glass plate without altering the position of the other, insofar as they are all on, one and the same conveyor.
In another connection, it was previously proposed in U.S. Pat. Nos. 4,364,766 and 4,475,937 that two convexing locations be juxtaposed on the same upper unit, one after the other in the longitudinal direction of feed of the conveyor. But the placement of the glass plates under each convexing location demands complicated means of delivery, so as to organize a correction of the delay of the glass plate the farthest up in relation to the one farthest down, thanks to detection systems, and means of logic, of independent conveyors. Thus, for each glass plate a new path and new speeds are to be defined. Furthermore, in spite of those complex means employed, there is no certainty of perfect positioning of the two glass plates at the end of travel under the upper unit, for, on the one hand, the detection of the glass plates is carried out at a relatively long distance from that end of travel and deviations and all kinds of disturbances can occur until the end of travel and, on the other, the optical detections, as proposed, are inaccurate at the high temperatures prevailing in the convexing installations.
Simplification of the system would lead to a need for a system capable of convexing glass plates possibly arriving at different instants under their convexing location, having followed different paths, the glass plates therefore being in different thermal states, thus resulting in convexing differences for those glass plates.